The PCP (Port Control Protocol) allows an IPv6 or IPv4 host to control how incoming IPv6 or IPv4 packets are translated and forwarded by a Network Address Translator (NAT) or simple firewall, and also allows a host to optimize its outgoing NAT keepalive messages. PCP was standardized as a successor to the NAT Port Mapping Protocol (NAT-PMP), with which it shares similar protocol concepts and packet formats.

By allowing applications to reduce the frequency of NAT keepalive messaging by using NAT PMP (PCP) to learn and influence the NAT mapping lifetime, bandwidth on the SM is optimized.